Ascaris lumbricoides is the most common helminth infection of humans worldwide and is the largest intestinal roundworm.Ascaris is a genus of
parasitic nematode worms. One species,
A. suum, typically infects
pigs, while another,
A. lumbricoides, affects human populations, typically in sub-tropical and tropical areas with poor sanitation. This infection is known as
ascariasis. Adult A.lumbricoides and A.suum live in the
small intestine. A female A.lumbricoides can produce up to 200,000 eggs a day, though the number of eggs produced per female worm is lower when there are large number of worms present in the gut, a phenomenon called density dependent fecundity. When an egg is passed into the environment it develops into a third stage larva in about 10 days, the rate depending on the temperature and relative humidity. This typically takes place on the soil, which is why A.lumbricoides is classified with
Trichuris trichiura and the hookworms
Necator americanus and
Ancylostoma duodenale as soil-transmitted helminths. It is estimated that some 1.2 billion people are infected with A.lumbricoides.
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